哪位高手能帮我看看错在哪里
定义：
向量相乘  对应位置的数相乘。(v1, v2)*(v3, v4) = (v1*v3, v2*v4)

向量与数相乘  向量每一个位置的数与该数相乘。(v1, v2)*a = (v1*a, v2*a)

数与向量相乘  数与向量中各维的平均数相乘。a*(v1,v2) = (a*v1, a*v2)

数与数相乘  两数的普通乘法。


#include <iostream>
#include <cstdlib>
#include <ctime>
#include <string>
#include <stdexcept>
using namespace std;
/*****************************************************/
class Vector;
class Number;

class Math{
public:
string toString(){return " ";}
string multiply(Vector *Vval){return " ";}
string multiply(Number *Nval){return " ";}
};

class Vector:public Math{
public:
Vector();
int GetVec(int i);
virtual string toString();
virtual string multiply(Vector &Vval);
virtual string multiply(Number &Nval);
private:
int vec[10];
};

class Number:public Math{
public:
Number();
int GetNum();
virtual string toString();
virtual string multiply(Vector &Vval);
virtual string multiply(Number &Nval);
private:
int num;
};

/*****************************************************/
void main()
{
srand((unsigned)time(NULL));
Vector a,b;
Number c,d;
Math* p[2]={&a, &c};

for (int i = 0; i < 2; i++)
{
//与向量相乘
cout < < "乘数: " < < p[i]-> toString() < < endl;
cout < < "被乘数: " < < b.toString() < < endl;
p[i]-> multiply(&b);//p[i]=p[i]*b;
cout < < "积: " < < p[i]-> toString() < < endl;

cout < < "--------------- " < < endl;

//与实数相乘
cout < < "乘数: " < < p[i]-> toString() < < endl;
cout < < "被乘数: " < < d.toString() < < endl;
p[i]-> multiply(&d);//p[i]=p[i]*d;
cout < < "积: " < < p[i]-> toString() < < endl;

cout < < "--------------- " < < endl;
}
system( "pause ");
}
/****************************************************/
Vector::Vector()
{
int temp;
for(int i = 0 ; i != 10 ; i++){
temp = rand()%20 + 1;
vec[i] = temp;
}
}

int Vector::GetVec(int i)
{
if(i <= 9 && i > = 0){
return vec[i];
}
else{
throw runtime_error( "i should be between 0 and 9 ");

}
}

string Vector::toString()
{
cout < < " <Vector> ";
for(int i = 0 ; i != 10 ; i++){
cout < <vec[i] < < " ";
}
cout < <endl;
return " ";
}

string Vector::multiply(Vector &Vval)
{
for(int i = 0 ; i != 10 ; i++){
vec[i] = vec[i] * Vval.GetVec(i);
}
return " ";
}

string Vector::multiply(Number &Nval)
{
for(int i = 0 ; i != 10 ; i++){
vec[i] = vec[i] * Nval.GetNum();
}
return " ";
}

/**********************************/

Number::Number()
{
num = rand()%20 + 1;
}

int Number::GetNum()
{
return num;
}

string Number::toString()
{
cout < < " <Number> ";
cout < <num < <endl;
return " ";
}

string Number::multiply(Vector &Vval)
{
int ave(0);
for(int i = 0 ; i != 10 ; i++){
ave += Vval.GetVec(i);
}
ave /= 10;
num *= ave;
return " ";
}

string Number::multiply(Number &Nval)
{
num *= Nval.GetNum();
return " ";
}

编译没有错误，但是没有达到预定的要求

[解决办法]
//sorry
=======
class Math{
public:
virtual string toString(){return " ";}
virtual string multiply(Vector& Vval){return " ";}
virtual string multiply(Number& Nval){return " ";}
};

[解决办法]
//楼主的错误...
//这个是以前的, 同样的功能, LZ参考下.
#include <iostream>
#include <string>
#include <strstream>
#include <ctime>
#include <vector>

using namespace std;


class Math
{
public:
Math(){};
~Math(){};

virtual string toString(){ return " "; }
virtual void multiply(Math* other) {}
virtual double mean() {return 0;}

virtual void GetData(vector <double> & _data){}
virtual void SetData(const vector <double> & _data) {}
};

class Number:public Math
{
public:
Number() { data = rand();}
~Number(){}

virtual string toString()
{
strstream stream;
stream < <data;
string str;
stream> > str;
return str;
}

virtual void multiply(Math* other)
{
data *= other-> mean();
}

virtual double mean() { return data;}

double GetData() { return data;}
void SetData( double _data) { data = _data;}

virtual void GetData(vector <double> & _data)
{ _data.push_back(data);}

virtual void SetData(const vector <double> & _data)
{if (_data.size()> 0) data = _data[0];}

private:

double data;
};


class Vector:public Math
{
public:
Vector()
{ for (int i=0; i <10; ++i) data[i] = rand();}
~Vector(){}

virtual string toString()
{
strstream stream;
stream < < "( ";
for (int i=0; i <9; ++i) {
stream < <data[i] < < ", ";
}
stream < <data[9] < < ") ";
string str;
stream> > str;
return str;
}

virtual void multiply(Math* other)
{
vector <double> vother;
other-> GetData(vother);
if (vother.size()==1) {
for (int i=0; i <10; ++i) data[i] *= vother[0];
}
else {
for (int i=0; i <10; ++i) data[i] *= vother[i];
}

}

virtual double mean()
{
double sum = 0;
for (int i=0; i <10; ++i) sum += data[i];
return sum /10;
}


virtual void GetData(vector <double> & _data)
{
for (int i=0; i <10; ++i) _data.push_back(data[i]);
}

virtual void SetData(const vector <double> & _data)
{
int _dataSize = _data.size();
for (int i=0; i < min(10, _dataSize); ++i) data[i] = _data[i];
}

private:

double data[10];
};


int main()
{
srand((unsigned)time(NULL));
Vector a,b;
Number c,d;
Math* p[2]={&a, &c};

for (int i = 0; i < 2; i++)
{
//与向量相乘
cout < < "乘数: " < < p[i]-> toString() < < endl;
cout < < "被乘数: " < < b.toString() < < endl;
p[i]-> multiply(&b);//p[i]=p[i]*b;
cout < < "积: " < < p[i]-> toString() < < endl;

cout < < "--------------- " < < endl;

//与实数相乘
cout < < "乘数: " < < p[i]-> toString() < < endl;
cout < < "被乘数: " < < d.toString() < < endl;
p[i]-> multiply(&d);//p[i]=p[i]*d;
cout < < "积: " < < p[i]-> toString() < < endl;

cout < < "--------------- " < < endl;
}

system( "pause ");
}

[解决办法]
其实是这样的，cout < < "乘数: " < < p[i]-> toString() < < endl;
< <运算符肯定是从左像右进行，但是在执行之前必须确保 < <运算符后面有参数，所以先要获得函数的返回值，就是说函数是最先执行的